It is known that aminobenzaldehydes such as p-dimethylaminobenzaldehyde (PDMAB) are useful in many colorimetric analyses. These analyses include tests for: urea; primary and secondary aromatic and aliphatic amines; aromatic nitro, nitroso, azo compounds, hydroxyproline, tryptophan, aminopeptidase in serum, pyruvic acid, and pyrogallol. In general, amines and their salts condense with PDMAB to yield colored Schiff bases according to the following reaction. ##STR1## With monoanimes, the Schiff bases are yellow whereas di- and polyamines yield orange Schiff bases. The reaction product has a more intense color when the reaction takes place in a dilute acid solution, due to the protonation of the --N.dbd.CH-- group.
PDMAB has also found use in fluorometric analyses; in the extraction of water insoluble alkaloids from the ergot fungus; and in the analyses of organic intermediates for the synthesis of hydrazine.
PDMAB, while extremely useful in these aforementioned tests, has one major drawback. The PDMAB reagent will readily oxidize with air contact in the dry form, and is also unstable in aqueous and acidic solutions.
Therefore, PDMAB has a short shelf life, and when acidified must be used immediately.
One aspect of this invention features a way of stabilizing aminobenzaldehydes such as PDMAB, and further teaches the synthesis of new and useful reagents derived from the stabilized aminobenzaldehyde base compound.